Electron detector with high backscattered electron acceptance for particle beam apparatus

Abstract

An electron detector for use in particle beam apparatus, providing particularly high acceptance of backscattered electrons. The electron detector includes an electron multiplier for detecting electrons and an electrode deployed between the electron multiplier and a specimen. The electrode is biased at a negative potential with respect to the specimen and also with respect to the electron multiplier.

What is claimed is: 
     
       1. An electron detector for detecting backscattered electrons emitted from a specimen, the electron detector comprising: (a) an electron multiplier having a front surface directed toward the specimen, said front surface releasing Type A secondary electrons on impingement of Type A backscattered electrons thereon, said Type A secondary electrons having trajectories away from said front surface; and   (b) an electrode deployed between said electron multiplier and the specimen, said electrode being biased at a negative potential with respect to both said front surface and the specimen and spaced from said front surface at a distance selected so as to generate an electric field which diverts said Type A secondary electrons towards said front surface.   
     
     
       2. The electron detector as in claim 1, wherein said front surface is biased at a positive potential with respect to the specimen. 
     
     
       3. The electron detector as in claim 1, wherein said front surface is biased at a negative potential with respect to the specimen. 
     
     
       4. The electron detector as in claim 1, wherein said front surface is biased at substantially the same potential as the specimen. 
     
     
       5. The electron detector as in claim 1, wherein said electron multiplier is a microchannel plate electron multiplier. 
     
     
       6. The electron detector as in claim 1, wherein said electron multiplier is a solid state electron multiplier. 
     
     
       7. The electron detector as in claim 1, wherein said electrode has a fixed diameter aperture selected for passing therethrough a solid angle of backscattered electrons for impingement on said front surface. 
     
     
       8. The electron detector as in claim 1, further comprising a beam shielding tube for passage therethrough of a particle beam toward the specimen, said beam shielding tube releasing Type B secondary electrons on impingement of Type B backscattered electrons thereon, said Type B secondary electrons having trajectories away from said beam shielding tube, said electric field diverting said Type B secondary electrons towards said front surface. 
     
     
       9. The electron detector as in claim 8, wherein said beam shielding tube has a beveled end. 
     
     
       10. The electron detector as in claim 8, wherein said front surface is biased at a positive potential with respect to said beam shielding tube. 
     
     
       11. The electron detector as in claim 8, wherein said electrode is biased at a negative potential with respect to said beam shielding tube. 
     
     
       12. The electron detector as in claim 8, wherein said electrode is biased at substantially the same potential as said beam shielding tube. 
     
     
       13. The electron detector as in claim 1, further comprising a second electrode interposed between said first electrode and the specimen for shielding the specimen from said electric field. 
     
     
       14. Particle beam apparatus including an electron detector for detecting backscattered electrons emitted from a specimen as claimed in claim 1. 
     
     
       15. An electron detector for detecting backscattered electrons emitted from a specimen, the electron detector comprising: (a) an electron multiplier having a front surface directed toward the specimen;   (b) a beam shielding tube for passage therethrough of a particle beam toward the specimen, said beam shielding tube releasing Type B secondary electrons on impingement of Type B backscattered electrons thereon, said Type B secondary electrons having trajectories away from said beam shielding tube; and   (c) an electrode deployed between said electron multiplier and the specimen, said electrode being biased at a negative potential with respect to both said front surface and the specimen and spaced from said front surface at a distance selected so as to generate an electric field which diverts said Type B secondary electrons towards said front surface.   
     
     
       16. The electron detector as in claim 15, wherein said front surface releases Type A secondary electrons on impingement of Type A backscattered electrons thereon, said Type A secondary electrons having trajectories away from said front surface and said electric field diverts said Type A secondary electrons towards said front surface. 
     
     
       17. The electron detector as in claim 15, wherein said front surface is biased at a positive potential with respect to the specimen. 
     
     
       18. The electron detector as in claim 15, wherein said front surface is biased at a negative potential with respect to the specimen. 
     
     
       19. The electron detector as in claim 15, wherein said front surface is biased at substantially the same potential as the specimen. 
     
     
       20. The electron detector as in claim 15, wherein said electron multiplier is a microchannel plate electron multiplier. 
     
     
       21. The electron detector as in claim 15, wherein said electron multiplier is a solid state electron multiplier. 
     
     
       22. The electron detector as in claim 15, wherein said electrode has a fixed diameter aperture selected for passing therethrough a solid angle of backscattered electrons for impingement on said front surface. 
     
     
       23. The electron detector as in claim 15, wherein said beam shielding tube has a beveled end. 
     
     
       24. The electron detector as in claim 15, wherein said front surface is biased at a positive potential with respect to said beam shielding tube. 
     
     
       25. The electron detector as in claim 15, wherein said electrode is biased at a negative potential with respect to said beam shielding tube. 
     
     
       26. The electron detector as in claim 15, wherein said electrode is biased at substantially the same potential as said beam shielding tube. 
     
     
       27. The electron detector as in claim 15, further comprising a second electrode interposed between said first electrode and the specimen for shielding the specimen from said electric field. 
     
     
       28. Particle beam apparatus including an electron detector for detecting backscattered electrons emitted from a specimen as claimed in claim 15. 
     
     
       29. An electron detector for detecting backscattered electrons emitted from a specimen, the electron detector comprising: (a) an electron multiplier having a front surface, said front surface releasing Type A secondary electrons on impingement of Type A backscattered electrons thereon, said Type A secondary electrons having trajectories away from said front surface; and   (b) an electrode being biased at a negative potential with respect to said front surface and spaced from said front surface at a distance selected so as to generate an electric field which diverts said Type A secondary electrons towards said front surface.